The present invention relates to a system for dispensing a continuous flow of viscous fluid and more particularly to a volumetric pump for dispensing a controlled and continuous flow of viscous fluid.
In many industrial manufacturing processes (e.g. the manufacturing process of electronic packages), there is the need to dispense a flow of viscous material. When this dispensing must produce a regular and thin thread (e.g. less than 1 mm diameter) the equipment must be able to provide a flow with a continuous and controlled dispensing rate. It is known to perform the above operation by means of a volumetric pump.
Two different types of volumetric pumps are currently available on the market. The first type is called an Auger valve pump, which uses an Archimede""s screw configuration. This kind of pump is suitable for dispensing constant volumes of material at constant temperature and constant viscosity. The results of these pumps strongly depend on the two parameters: temperature and viscosity; if these change, the dispensed flow will be different. For the above problem, these pumps are also known as xe2x80x9cPseudo-volumetric pumpsxe2x80x9d. Functionally, these pumps have an helicoidal chamber with an endless screw that pushes the material through an outlet. This kind of pump is prone to failure if the material to be dispensed has a non optimized Theological behavior. These pumps are only suitable for those materials having good rheological properties, because they need to bear the stress and the deformation caused by applied mechanical forces, that make the materials flow in a rather long and complex path. The combination of pressure and attrition may break the material (e.g. gel compositions may break into their main subconstituents when undergoing mechanical attrition and pressure); that is, the material may change its physical properties. These pumps are available for materials with a viscosity above 100,000 cps (i.e. centipoise) and for a maximum dispensing rate of 10 mg/sec.
The second type of pump available on the market is called a Linear or Positive Displacements piston pump. These pumps have a loading chamber and a pushing piston. Material is loaded and dispensed through a single piston movement that alternatively loads by sucking up the material from a reservoir when it moves back in the chamber and pushes the material out when the piston moves forward. These pumps force the user either to: (1) experience delays in the dispensing operation while the pump at the end of one piston revolution has to reload material to continue the dispensing operation; or (2) use a multiple pump configuration to guarantee a continuous flow of material.
It is an object of the present invention to provide a technique which overcomes the above drawbacks.
According to the present invention, we provide a pump for dispensing viscous fluid comprising a chamber including an inlet aperture, being connectable with a reservoir, and a dispensing outlet aperture, a first and a second piston within said chamber, said first and said second piston being movable in anti-phase, said first piston, in use, reciprocating to periodically open and close said inlet aperture and said second piston, in use, reciprocating to periodically open and close said outlet aperture.